As an example of a sensor having a sensor element to detect a gas under measurement, conventionally known is an oxygen sensor for measuring the concentration of oxygen in an automotive exhaust gas. There is known a sensor element for use in such an oxygen sensor, including a bottomed cylindrical solid electrolyte body, an inner electrode formed on an inner side of the solid electrolyte body and an outer electrode formed on an outer side of the solid electrolyte body, as disclosed in Patent Documents 1 and 2.
An inner connection terminal is fitted into a rear end portion of the sensor element and electrically connected to the inner electrode (of the sensor element). A sensor output lead is connected to a rear end portion of the inner connection terminal. In the case where a rod-shaped ceramic heater is inserted in the sensor element, the inner connection terminal is attached around the ceramic heater.
An outer connection terminal (ground connection terminal) is fitted onto the rear end portion of the sensor element and electrically connected to the outer electrode (of the sensor element). A ground lead is connected to a rear end portion of the outer connection terminal.
As shown in FIG. 13(a), the outer connection terminal P1 generally includes a cylindrical outer fitting portion P2 (having left and right wing sections) for contact with the sensor element from outside and an elongated extension portion P3 extending axially from a rear end (in the drawing, an upper end) of the outer fitting portion P2 (for connection with the lead).
On the other hand, the inner connection terminal P4 includes a cylindrical inner fitting portion P5 (having left and right wing sections) for contact with the sensor element from inside and an elongated extension portion P6 extending axially from a rear end of the inner fitting portion P5 (for connection with the lead) as shown in FIG. 13(b).
As shown in FIG. 13(c), a cylindrical separator P7 is provided with axial through holes P8 and P9 such that the extension portion P3 of the outer connection terminal P1 and the extension portion P6 of the inner connection terminal P4 are inserted and pass the through holes P8 and P9, respectively.